includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use InvalidArgumentException;
  32 use RuntimeException;
  33 use Exception;
  34
  35 /**
  36  * Database connection, tracking, load balancing, and transaction manager for a cluster
  37  *
  38  * @ingroup Database
  39  */
  40 class LoadBalancer implements ILoadBalancer {
  41         /** @var array[] Map of (server index => server config array) */
  42         private $mServers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $mConns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $mLoads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $mGroupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $mAllowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $mWaitTimeout;
  53         /** @var array The LoadMonitor configuration */
  54         private $loadMonitorConfig;
  55         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  56         private $tableAliases = [];
  57
  58         /** @var ILoadMonitor */
  59         private $loadMonitor;
  60         /** @var ChronologyProtector|null */
  61         private $chronProt;
  62         /** @var BagOStuff */
  63         private $srvCache;
  64         /** @var WANObjectCache */
  65         private $wanCache;
  66         /** @var object|string Class name or object With profileIn/profileOut methods */
  67         protected $profiler;
  68         /** @var TransactionProfiler */
  69         protected $trxProfiler;
  70         /** @var LoggerInterface */
  71         protected $replLogger;
  72         /** @var LoggerInterface */
  73         protected $connLogger;
  74         /** @var LoggerInterface */
  75         protected $queryLogger;
  76         /** @var LoggerInterface */
  77         protected $perfLogger;
  78
  79         /** @var Database DB connection object that caused a problem */
  80         private $errorConnection;
  81         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
  82         private $mReadIndex;
  83         /** @var bool|DBMasterPos False if not set */
  84         private $mWaitForPos;
  85         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  86         private $laggedReplicaMode = false;
  87         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  88         private $allReplicasDownMode = false;
  89         /** @var string The last DB selection or connection error */
  90         private $mLastError = 'Unknown error';
  91         /** @var string|bool Reason the LB is read-only or false if not */
  92         private $readOnlyReason = false;
  93         /** @var int Total connections opened */
  94         private $connsOpened = 0;
  95         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  96         private $trxRoundId = false;
  97         /** @var array[] Map of (name => callable) */
  98         private $trxRecurringCallbacks = [];
  99         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 100         private $localDomain;
 101         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 102         private $localDomainIdAlias;
 103         /** @var string Current server name */
 104         private $host;
 105         /** @var bool Whether this PHP instance is for a CLI script */
 106         protected $cliMode;
 107         /** @var string Agent name for query profiling */
 108         protected $agent;
 109
 110         /** @var callable Exception logger */
 111         private $errorLogger;
 112
 113         /** @var bool */
 114         private $disabled = false;
 115         /** @var bool */
 116         private $chronProtInitialized = false;
 117         /** @var int */
 118         private $maxLag = self::MAX_LAG_DEFAULT;
 119
 120         /** @var int Warn when this many connection are held */
 121         const CONN_HELD_WARN_THRESHOLD = 10;
 122
 123         /** @var int Default 'maxLag' when unspecified */
 124         const MAX_LAG_DEFAULT = 10;
 125         /** @var int Seconds to cache master server read-only status */
 126         const TTL_CACHE_READONLY = 5;
 127
 128         const KEY_LOCAL = 'local';
 129         const KEY_FOREIGN_FREE = 'foreignFree';
 130         const KEY_FOREIGN_INUSE = 'foreignInUse';
 131
 132         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 133         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 134         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 135
 136         public function __construct( array $params ) {
 137                 if ( !isset( $params['servers'] ) ) {
 138                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 139                 }
 140                 $this->mServers = $params['servers'];
 141                 foreach ( $this->mServers as $i => $server ) {
 142                         if ( $i == 0 ) {
 143                                 $this->mServers[$i]['master'] = true;
 144                         } else {
 145                                 $this->mServers[$i]['replica'] = true;
 146                         }
 147                 }
 148
 149                 $this->localDomain = isset( $params['localDomain'] )
 150                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 151                         : DatabaseDomain::newUnspecified();
 152                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 153                 // always true, gracefully handle the case when they fail to account for escaping.
 154                 if ( $this->localDomain->getTablePrefix() != '' ) {
 155                         $this->localDomainIdAlias =
 156                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 157                 } else {
 158                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 159                 }
 160
 161                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 162
 163                 $this->mReadIndex = -1;
 164                 $this->mConns = [
 165                         // Connection were transaction rounds may be applied
 166                         self::KEY_LOCAL => [],
 167                         self::KEY_FOREIGN_INUSE => [],
 168                         self::KEY_FOREIGN_FREE => [],
 169                         // Auto-committing counterpart connections that ignore transaction rounds
 170                         self::KEY_LOCAL_NOROUND => [],
 171                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 172                         self::KEY_FOREIGN_FREE_NOROUND => []
 173                 ];
 174                 $this->mLoads = [];
 175                 $this->mWaitForPos = false;
 176                 $this->mAllowLagged = false;
 177
 178                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 179                         $this->readOnlyReason = $params['readOnlyReason'];
 180                 }
 181
 182                 if ( isset( $params['maxLag'] ) ) {
 183                         $this->maxLag = $params['maxLag'];
 184                 }
 185
 186                 if ( isset( $params['loadMonitor'] ) ) {
 187                         $this->loadMonitorConfig = $params['loadMonitor'];
 188                 } else {
 189                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 190                 }
 191                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 192
 193                 foreach ( $params['servers'] as $i => $server ) {
 194                         $this->mLoads[$i] = $server['load'];
 195                         if ( isset( $server['groupLoads'] ) ) {
 196                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 197                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 198                                                 $this->mGroupLoads[$group] = [];
 199                                         }
 200                                         $this->mGroupLoads[$group][$i] = $ratio;
 201                                 }
 202                         }
 203                 }
 204
 205                 if ( isset( $params['srvCache'] ) ) {
 206                         $this->srvCache = $params['srvCache'];
 207                 } else {
 208                         $this->srvCache = new EmptyBagOStuff();
 209                 }
 210                 if ( isset( $params['wanCache'] ) ) {
 211                         $this->wanCache = $params['wanCache'];
 212                 } else {
 213                         $this->wanCache = WANObjectCache::newEmpty();
 214                 }
 215                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 216                 if ( isset( $params['trxProfiler'] ) ) {
 217                         $this->trxProfiler = $params['trxProfiler'];
 218                 } else {
 219                         $this->trxProfiler = new TransactionProfiler();
 220                 }
 221
 222                 $this->errorLogger = isset( $params['errorLogger'] )
 223                         ? $params['errorLogger']
 224                         : function ( Exception $e ) {
 225                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 226                         };
 227
 228                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 229                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 230                 }
 231
 232                 $this->host = isset( $params['hostname'] )
 233                         ? $params['hostname']
 234                         : ( gethostname() ?: 'unknown' );
 235                 $this->cliMode = isset( $params['cliMode'] )
 236                         ? $params['cliMode']
 237                         : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 238                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 239
 240                 if ( isset( $params['chronologyProtector'] ) ) {
 241                         $this->chronProt = $params['chronologyProtector'];
 242                 }
 243         }
 244
 245         /**
 246          * Get a LoadMonitor instance
 247          *
 248          * @return ILoadMonitor
 249          */
 250         private function getLoadMonitor() {
 251                 if ( !isset( $this->loadMonitor ) ) {
 252                         $compat = [
 253                                 'LoadMonitor' => LoadMonitor::class,
 254                                 'LoadMonitorNull' => LoadMonitorNull::class,
 255                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 256                         ];
 257
 258                         $class = $this->loadMonitorConfig['class'];
 259                         if ( isset( $compat[$class] ) ) {
 260                                 $class = $compat[$class];
 261                         }
 262
 263                         $this->loadMonitor = new $class(
 264                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 265                         $this->loadMonitor->setLogger( $this->replLogger );
 266                 }
 267
 268                 return $this->loadMonitor;
 269         }
 270
 271         /**
 272          * @param array $loads
 273          * @param bool|string $domain Domain to get non-lagged for
 274          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 275          * @return bool|int|string
 276          */
 277         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 278                 $lags = $this->getLagTimes( $domain );
 279
 280                 # Unset excessively lagged servers
 281                 foreach ( $lags as $i => $lag ) {
 282                         if ( $i != 0 ) {
 283                                 # How much lag this server nominally is allowed to have
 284                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 285                                         ? $this->mServers[$i]['max lag']
 286                                         : $this->maxLag; // default
 287                                 # Constrain that futher by $maxLag argument
 288                                 $maxServerLag = min( $maxServerLag, $maxLag );
 289
 290                                 $host = $this->getServerName( $i );
 291                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 292                                         $this->replLogger->error(
 293                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 294                                         unset( $loads[$i] );
 295                                 } elseif ( $lag > $maxServerLag ) {
 296                                         $this->replLogger->info(
 297                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 298                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 299                                         );
 300                                         unset( $loads[$i] );
 301                                 }
 302                         }
 303                 }
 304
 305                 # Find out if all the replica DBs with non-zero load are lagged
 306                 $sum = 0;
 307                 foreach ( $loads as $load ) {
 308                         $sum += $load;
 309                 }
 310                 if ( $sum == 0 ) {
 311                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 312                         # Do NOT use the master
 313                         # Instead, this function will return false, triggering read-only mode,
 314                         # and a lagged replica DB will be used instead.
 315                         return false;
 316                 }
 317
 318                 if ( count( $loads ) == 0 ) {
 319                         return false;
 320                 }
 321
 322                 # Return a random representative of the remainder
 323                 return ArrayUtils::pickRandom( $loads );
 324         }
 325
 326         public function getReaderIndex( $group = false, $domain = false ) {
 327                 if ( count( $this->mServers ) == 1 ) {
 328                         // Skip the load balancing if there's only one server
 329                         return $this->getWriterIndex();
 330                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 331                         // Shortcut if the generic reader index was already cached
 332                         return $this->mReadIndex;
 333                 }
 334
 335                 if ( $group !== false ) {
 336                         // Use the server weight array for this load group
 337                         if ( isset( $this->mGroupLoads[$group] ) ) {
 338                                 $loads = $this->mGroupLoads[$group];
 339                         } else {
 340                                 // No loads for this group, return false and the caller can use some other group
 341                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 342
 343                                 return false;
 344                         }
 345                 } else {
 346                         // Use the generic load group
 347                         $loads = $this->mLoads;
 348                 }
 349
 350                 // Scale the configured load ratios according to each server's load and state
 351                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 352
 353                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 354                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 355                 if ( $i === false ) {
 356                         // Replica DB connection unsuccessful
 357                         return false;
 358                 }
 359
 360                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 361                         // Before any data queries are run, wait for the server to catch up to the
 362                         // specified position. This is used to improve session consistency. Note that
 363                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 364                         // so update laggedReplicaMode as needed for consistency.
 365                         if ( !$this->doWait( $i ) ) {
 366                                 $laggedReplicaMode = true;
 367                         }
 368                 }
 369
 370                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 371                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 372                         $this->mReadIndex = $i;
 373                         // Record if the generic reader index is in "lagged replica DB" mode
 374                         if ( $laggedReplicaMode ) {
 375                                 $this->laggedReplicaMode = true;
 376                         }
 377                 }
 378
 379                 $serverName = $this->getServerName( $i );
 380                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 381
 382                 return $i;
 383         }
 384
 385         /**
 386          * @param array $loads List of server weights
 387          * @param string|bool $domain
 388          * @return array (reader index, lagged replica mode) or false on failure
 389          */
 390         private function pickReaderIndex( array $loads, $domain = false ) {
 391                 if ( !count( $loads ) ) {
 392                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 393                 }
 394
 395                 /** @var int|bool $i Index of selected server */
 396                 $i = false;
 397                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 398                 $laggedReplicaMode = false;
 399
 400                 // Quickly look through the available servers for a server that meets criteria...
 401                 $currentLoads = $loads;
 402                 while ( count( $currentLoads ) ) {
 403                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 404                                 $i = ArrayUtils::pickRandom( $currentLoads );
 405                         } else {
 406                                 $i = false;
 407                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 408                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 409                                         // This triggers doWait() after connect, so it's especially good to
 410                                         // avoid lagged servers so as to avoid excessive delay in that method.
 411                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 412                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 413                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 414                                 }
 415                                 if ( $i === false ) {
 416                                         // Any server with less lag than it's 'max lag' param is preferable
 417                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 418                                 }
 419                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 420                                         // All replica DBs lagged. Switch to read-only mode
 421                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 422                                         $i = ArrayUtils::pickRandom( $currentLoads );
 423                                         $laggedReplicaMode = true;
 424                                 }
 425                         }
 426
 427                         if ( $i === false ) {
 428                                 // pickRandom() returned false.
 429                                 // This is permanent and means the configuration or the load monitor
 430                                 // wants us to return false.
 431                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 432
 433                                 return [ false, false ];
 434                         }
 435
 436                         $serverName = $this->getServerName( $i );
 437                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 438
 439                         $conn = $this->openConnection( $i, $domain );
 440                         if ( !$conn ) {
 441                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 442                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 443                                 $i = false;
 444                                 continue;
 445                         }
 446
 447                         // Decrement reference counter, we are finished with this connection.
 448                         // It will be incremented for the caller later.
 449                         if ( $domain !== false ) {
 450                                 $this->reuseConnection( $conn );
 451                         }
 452
 453                         // Return this server
 454                         break;
 455                 }
 456
 457                 // If all servers were down, quit now
 458                 if ( !count( $currentLoads ) ) {
 459                         $this->connLogger->error( "All servers down" );
 460                 }
 461
 462                 return [ $i, $laggedReplicaMode ];
 463         }
 464
 465         public function waitFor( $pos ) {
 466                 $oldPos = $this->mWaitForPos;
 467                 try {
 468                         $this->mWaitForPos = $pos;
 469                         // If a generic reader connection was already established, then wait now
 470                         $i = $this->mReadIndex;
 471                         if ( $i > 0 ) {
 472                                 if ( !$this->doWait( $i ) ) {
 473                                         $this->laggedReplicaMode = true;
 474                                 }
 475                         }
 476                 } finally {
 477                         // Restore the older position if it was higher since this is used for lag-protection
 478                         $this->setWaitForPositionIfHigher( $oldPos );
 479                 }
 480         }
 481
 482         public function waitForOne( $pos, $timeout = null ) {
 483                 $oldPos = $this->mWaitForPos;
 484                 try {
 485                         $this->mWaitForPos = $pos;
 486
 487                         $i = $this->mReadIndex;
 488                         if ( $i <= 0 ) {
 489                                 // Pick a generic replica DB if there isn't one yet
 490                                 $readLoads = $this->mLoads;
 491                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 492                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 493                                 $i = ArrayUtils::pickRandom( $readLoads );
 494                         }
 495
 496                         if ( $i > 0 ) {
 497                                 $ok = $this->doWait( $i, true, $timeout );
 498                         } else {
 499                                 $ok = true; // no applicable loads
 500                         }
 501                 } finally {
 502                         # Restore the old position, as this is not used for lag-protection but for throttling
 503                         $this->mWaitForPos = $oldPos;
 504                 }
 505
 506                 return $ok;
 507         }
 508
 509         public function waitForAll( $pos, $timeout = null ) {
 510                 $oldPos = $this->mWaitForPos;
 511                 try {
 512                         $this->mWaitForPos = $pos;
 513                         $serverCount = count( $this->mServers );
 514
 515                         $ok = true;
 516                         for ( $i = 1; $i < $serverCount; $i++ ) {
 517                                 if ( $this->mLoads[$i] > 0 ) {
 518                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 519                                 }
 520                         }
 521                 } finally {
 522                         # Restore the old position, as this is not used for lag-protection but for throttling
 523                         $this->mWaitForPos = $oldPos;
 524                 }
 525
 526                 return $ok;
 527         }
 528
 529         /**
 530          * @param DBMasterPos|bool $pos
 531          */
 532         private function setWaitForPositionIfHigher( $pos ) {
 533                 if ( !$pos ) {
 534                         return;
 535                 }
 536
 537                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 538                         $this->mWaitForPos = $pos;
 539                 }
 540         }
 541
 542         /**
 543          * @param int $i
 544          * @return IDatabase|bool
 545          */
 546         public function getAnyOpenConnection( $i ) {
 547                 foreach ( $this->mConns as $connsByServer ) {
 548                         if ( !empty( $connsByServer[$i] ) ) {
 549                                 /** @var IDatabase[] $serverConns */
 550                                 $serverConns = $connsByServer[$i];
 551
 552                                 return reset( $serverConns );
 553                         }
 554                 }
 555
 556                 return false;
 557         }
 558
 559         /**
 560          * Wait for a given replica DB to catch up to the master pos stored in $this
 561          * @param int $index Server index
 562          * @param bool $open Check the server even if a new connection has to be made
 563          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 564          * @return bool
 565          */
 566         protected function doWait( $index, $open = false, $timeout = null ) {
 567                 $close = false; // close the connection afterwards
 568
 569                 // Check if we already know that the DB has reached this point
 570                 $server = $this->getServerName( $index );
 571                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 572                 /** @var DBMasterPos $knownReachedPos */
 573                 $knownReachedPos = $this->srvCache->get( $key );
 574                 if (
 575                         $knownReachedPos instanceof DBMasterPos &&
 576                         $knownReachedPos->hasReached( $this->mWaitForPos )
 577                 ) {
 578                         $this->replLogger->debug( __METHOD__ .
 579                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 580                                 [ 'dbserver' => $server ] );
 581                         return true;
 582                 }
 583
 584                 // Find a connection to wait on, creating one if needed and allowed
 585                 $conn = $this->getAnyOpenConnection( $index );
 586                 if ( !$conn ) {
 587                         if ( !$open ) {
 588                                 $this->replLogger->debug( __METHOD__ . ': no connection open for {dbserver}',
 589                                         [ 'dbserver' => $server ] );
 590
 591                                 return false;
 592                         } else {
 593                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 594                                 if ( !$conn ) {
 595                                         $this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
 596                                                 [ 'dbserver' => $server ] );
 597
 598                                         return false;
 599                                 }
 600                                 // Avoid connection spam in waitForAll() when connections
 601                                 // are made just for the sake of doing this lag check.
 602                                 $close = true;
 603                         }
 604                 }
 605
 606                 $this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
 607                         [ 'dbserver' => $server ] );
 608                 $timeout = $timeout ?: $this->mWaitTimeout;
 609                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 610
 611                 if ( $result == -1 || is_null( $result ) ) {
 612                         // Timed out waiting for replica DB, use master instead
 613                         $this->replLogger->warning(
 614                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 615                                 [ 'host' => $server, 'pos' => $this->mWaitForPos ]
 616                         );
 617                         $ok = false;
 618                 } else {
 619                         $this->replLogger->info( __METHOD__ . ": Done" );
 620                         $ok = true;
 621                         // Remember that the DB reached this point
 622                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 623                 }
 624
 625                 if ( $close ) {
 626                         $this->closeConnection( $conn );
 627                 }
 628
 629                 return $ok;
 630         }
 631
 632         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 633                 if ( $i === null || $i === false ) {
 634                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 635                                 ' with invalid server index' );
 636                 }
 637
 638                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 639                         $domain = false; // local connection requested
 640                 }
 641
 642                 $groups = ( $groups === false || $groups === [] )
 643                         ? [ false ] // check one "group": the generic pool
 644                         : (array)$groups;
 645
 646                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 647                 $oldConnsOpened = $this->connsOpened; // connections open now
 648
 649                 if ( $i == self::DB_MASTER ) {
 650                         $i = $this->getWriterIndex();
 651                 } else {
 652                         # Try to find an available server in any the query groups (in order)
 653                         foreach ( $groups as $group ) {
 654                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 655                                 if ( $groupIndex !== false ) {
 656                                         $i = $groupIndex;
 657                                         break;
 658                                 }
 659                         }
 660                 }
 661
 662                 # Operation-based index
 663                 if ( $i == self::DB_REPLICA ) {
 664                         $this->mLastError = 'Unknown error'; // reset error string
 665                         # Try the general server pool if $groups are unavailable.
 666                         $i = ( $groups === [ false ] )
 667                                 ? false // don't bother with this if that is what was tried above
 668                                 : $this->getReaderIndex( false, $domain );
 669                         # Couldn't find a working server in getReaderIndex()?
 670                         if ( $i === false ) {
 671                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 672                                 // Throw an exception
 673                                 $this->reportConnectionError();
 674                                 return null; // not reached
 675                         }
 676                 }
 677
 678                 # Now we have an explicit index into the servers array
 679                 $conn = $this->openConnection( $i, $domain, $flags );
 680                 if ( !$conn ) {
 681                         // Throw an exception
 682                         $this->reportConnectionError();
 683                         return null; // not reached
 684                 }
 685
 686                 # Profile any new connections that happen
 687                 if ( $this->connsOpened > $oldConnsOpened ) {
 688                         $host = $conn->getServer();
 689                         $dbname = $conn->getDBname();
 690                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 691                 }
 692
 693                 if ( $masterOnly ) {
 694                         # Make master-requested DB handles inherit any read-only mode setting
 695                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 696                 }
 697
 698                 return $conn;
 699         }
 700
 701         public function reuseConnection( $conn ) {
 702                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 703                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 704                 if ( $serverIndex === null || $refCount === null ) {
 705                         /**
 706                          * This can happen in code like:
 707                          *   foreach ( $dbs as $db ) {
 708                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 709                          *     ...
 710                          *     $lb->reuseConnection( $conn );
 711                          *   }
 712                          * When a connection to the local DB is opened in this way, reuseConnection()
 713                          * should be ignored
 714                          */
 715                         return;
 716                 } elseif ( $conn instanceof DBConnRef ) {
 717                         // DBConnRef already handles calling reuseConnection() and only passes the live
 718                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 719                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 720                                 ( new RuntimeException() )->getTraceAsString() );
 721
 722                         return;
 723                 }
 724
 725                 if ( $this->disabled ) {
 726                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 727                 }
 728
 729                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 730                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 731                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 732                 } else {
 733                         $connFreeKey = self::KEY_FOREIGN_FREE;
 734                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 735                 }
 736
 737                 $domain = $conn->getDomainID();
 738                 if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 739                         throw new InvalidArgumentException( __METHOD__ .
 740                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 741                 } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 742                         throw new InvalidArgumentException( __METHOD__ .
 743                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 744                 }
 745
 746                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 747                 if ( $refCount <= 0 ) {
 748                         $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
 749                         unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
 750                         if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
 751                                 unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 752                         }
 753                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 754                 } else {
 755                         $this->connLogger->debug( __METHOD__ .
 756                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 757                 }
 758         }
 759
 760         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 761                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 762
 763                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 764         }
 765
 766         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 767                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 768
 769                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 770         }
 771
 772         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 773                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 774
 775                 return new MaintainableDBConnRef(
 776                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 777         }
 778
 779         public function openConnection( $i, $domain = false, $flags = 0 ) {
 780                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 781                         $domain = false; // local connection requested
 782                 }
 783
 784                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 785                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 786                         // Load CP positions before connecting so that doWait() triggers later if needed
 787                         $this->chronProtInitialized = true;
 788                         $this->chronProt->initLB( $this );
 789                 }
 790
 791                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 792                 // main set of DB connections but rather its own pool since:
 793                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 794                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 795                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 796
 797                 if ( $domain !== false ) {
 798                         // Connection is to a foreign domain
 799                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 800                 } else {
 801                         // Connection is to the local domain
 802                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 803                         if ( isset( $this->mConns[$connKey][$i][0] ) ) {
 804                                 $conn = $this->mConns[$connKey][$i][0];
 805                         } else {
 806                                 if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 807                                         throw new InvalidArgumentException( "No server with index '$i'." );
 808                                 }
 809                                 // Open a new connection
 810                                 $server = $this->mServers[$i];
 811                                 $server['serverIndex'] = $i;
 812                                 $server['autoCommitOnly'] = $autoCommit;
 813                                 $conn = $this->reallyOpenConnection( $server, false );
 814                                 $host = $this->getServerName( $i );
 815                                 if ( $conn->isOpen() ) {
 816                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 817                                         $this->mConns[$connKey][$i][0] = $conn;
 818                                 } else {
 819                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 820                                         $this->errorConnection = $conn;
 821                                         $conn = false;
 822                                 }
 823                         }
 824                 }
 825
 826                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 827                         // Connection was made but later unrecoverably lost for some reason.
 828                         // Do not return a handle that will just throw exceptions on use,
 829                         // but let the calling code (e.g. getReaderIndex) try another server.
 830                         // See DatabaseMyslBase::ping() for how this can happen.
 831                         $this->errorConnection = $conn;
 832                         $conn = false;
 833                 }
 834
 835                 if ( $autoCommit && $conn instanceof IDatabase ) {
 836                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 837                 }
 838
 839                 return $conn;
 840         }
 841
 842         /**
 843          * Open a connection to a foreign DB, or return one if it is already open.
 844          *
 845          * Increments a reference count on the returned connection which locks the
 846          * connection to the requested domain. This reference count can be
 847          * decremented by calling reuseConnection().
 848          *
 849          * If a connection is open to the appropriate server already, but with the wrong
 850          * database, it will be switched to the right database and returned, as long as
 851          * it has been freed first with reuseConnection().
 852          *
 853          * On error, returns false, and the connection which caused the
 854          * error will be available via $this->errorConnection.
 855          *
 856          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 857          *
 858          * @param int $i Server index
 859          * @param string $domain Domain ID to open
 860          * @param int $flags Class CONN_* constant bitfield
 861          * @return Database
 862          */
 863         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 864                 $domainInstance = DatabaseDomain::newFromId( $domain );
 865                 $dbName = $domainInstance->getDatabase();
 866                 $prefix = $domainInstance->getTablePrefix();
 867                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 868
 869                 if ( $autoCommit ) {
 870                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 871                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 872                 } else {
 873                         $connFreeKey = self::KEY_FOREIGN_FREE;
 874                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 875                 }
 876
 877                 if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
 878                         // Reuse an in-use connection for the same domain
 879                         $conn = $this->mConns[$connInUseKey][$i][$domain];
 880                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 881                 } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 882                         // Reuse a free connection for the same domain
 883                         $conn = $this->mConns[$connFreeKey][$i][$domain];
 884                         unset( $this->mConns[$connFreeKey][$i][$domain] );
 885                         $this->mConns[$connInUseKey][$i][$domain] = $conn;
 886                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 887                 } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
 888                         // Reuse a free connection from another domain
 889                         $conn = reset( $this->mConns[$connFreeKey][$i] );
 890                         $oldDomain = key( $this->mConns[$connFreeKey][$i] );
 891                         // The empty string as a DB name means "don't care".
 892                         // DatabaseMysqlBase::open() already handle this on connection.
 893                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 894                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 895                                         $conn->getServer() . " from client host {$this->host}";
 896                                 $this->errorConnection = $conn;
 897                                 $conn = false;
 898                         } else {
 899                                 $conn->tablePrefix( $prefix );
 900                                 unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
 901                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 902                                 $this->connLogger->debug( __METHOD__ .
 903                                         ": reusing free connection from $oldDomain for $domain" );
 904                         }
 905                 } else {
 906                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 907                                 throw new InvalidArgumentException( "No server with index '$i'." );
 908                         }
 909                         // Open a new connection
 910                         $server = $this->mServers[$i];
 911                         $server['serverIndex'] = $i;
 912                         $server['foreignPoolRefCount'] = 0;
 913                         $server['foreign'] = true;
 914                         $server['autoCommitOnly'] = $autoCommit;
 915                         $conn = $this->reallyOpenConnection( $server, $dbName );
 916                         if ( !$conn->isOpen() ) {
 917                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 918                                 $this->errorConnection = $conn;
 919                                 $conn = false;
 920                         } else {
 921                                 $conn->tablePrefix( $prefix );
 922                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 923                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 924                         }
 925                 }
 926
 927                 // Increment reference count
 928                 if ( $conn instanceof IDatabase ) {
 929                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 930                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 931                 }
 932
 933                 return $conn;
 934         }
 935
 936         /**
 937          * Test if the specified index represents an open connection
 938          *
 939          * @param int $index Server index
 940          * @access private
 941          * @return bool
 942          */
 943         private function isOpen( $index ) {
 944                 if ( !is_int( $index ) ) {
 945                         return false;
 946                 }
 947
 948                 return (bool)$this->getAnyOpenConnection( $index );
 949         }
 950
 951         /**
 952          * Really opens a connection. Uncached.
 953          * Returns a Database object whether or not the connection was successful.
 954          * @access private
 955          *
 956          * @param array $server
 957          * @param string|bool $dbNameOverride Use "" to not select any database
 958          * @return Database
 959          * @throws DBAccessError
 960          * @throws InvalidArgumentException
 961          */
 962         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 963                 if ( $this->disabled ) {
 964                         throw new DBAccessError();
 965                 }
 966
 967                 if ( $dbNameOverride !== false ) {
 968                         $server['dbname'] = $dbNameOverride;
 969                 }
 970
 971                 // Let the handle know what the cluster master is (e.g. "db1052")
 972                 $masterName = $this->getServerName( $this->getWriterIndex() );
 973                 $server['clusterMasterHost'] = $masterName;
 974
 975                 // Log when many connection are made on requests
 976                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 977                         $this->perfLogger->warning( __METHOD__ . ": " .
 978                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 979                 }
 980
 981                 $server['srvCache'] = $this->srvCache;
 982                 // Set loggers and profilers
 983                 $server['connLogger'] = $this->connLogger;
 984                 $server['queryLogger'] = $this->queryLogger;
 985                 $server['errorLogger'] = $this->errorLogger;
 986                 $server['profiler'] = $this->profiler;
 987                 $server['trxProfiler'] = $this->trxProfiler;
 988                 // Use the same agent and PHP mode for all DB handles
 989                 $server['cliMode'] = $this->cliMode;
 990                 $server['agent'] = $this->agent;
 991                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 992                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 993                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 994
 995                 // Create a live connection object
 996                 try {
 997                         $db = Database::factory( $server['type'], $server );
 998                 } catch ( DBConnectionError $e ) {
 999                         // FIXME: This is probably the ugliest thing I have ever done to
1000                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1001                         $db = $e->db;
1002                 }
1003
1004                 $db->setLBInfo( $server );
1005                 $db->setLazyMasterHandle(
1006                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1007                 );
1008                 $db->setTableAliases( $this->tableAliases );
1009
1010                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1011                         if ( $this->trxRoundId !== false ) {
1012                                 $this->applyTransactionRoundFlags( $db );
1013                         }
1014                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1015                                 $db->setTransactionListener( $name, $callback );
1016                         }
1017                 }
1018
1019                 return $db;
1020         }
1021
1022         /**
1023          * @throws DBConnectionError
1024          */
1025         private function reportConnectionError() {
1026                 $conn = $this->errorConnection; // the connection which caused the error
1027                 $context = [
1028                         'method' => __METHOD__,
1029                         'last_error' => $this->mLastError,
1030                 ];
1031
1032                 if ( $conn instanceof IDatabase ) {
1033                         $context['db_server'] = $conn->getServer();
1034                         $this->connLogger->warning(
1035                                 "Connection error: {last_error} ({db_server})",
1036                                 $context
1037                         );
1038
1039                         // throws DBConnectionError
1040                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
1041                 } else {
1042                         // No last connection, probably due to all servers being too busy
1043                         $this->connLogger->error(
1044                                 "LB failure with no last connection. Connection error: {last_error}",
1045                                 $context
1046                         );
1047
1048                         // If all servers were busy, mLastError will contain something sensible
1049                         throw new DBConnectionError( null, $this->mLastError );
1050                 }
1051         }
1052
1053         public function getWriterIndex() {
1054                 return 0;
1055         }
1056
1057         public function haveIndex( $i ) {
1058                 return array_key_exists( $i, $this->mServers );
1059         }
1060
1061         public function isNonZeroLoad( $i ) {
1062                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1063         }
1064
1065         public function getServerCount() {
1066                 return count( $this->mServers );
1067         }
1068
1069         public function getServerName( $i ) {
1070                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1071                         $name = $this->mServers[$i]['hostName'];
1072                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1073                         $name = $this->mServers[$i]['host'];
1074                 } else {
1075                         $name = '';
1076                 }
1077
1078                 return ( $name != '' ) ? $name : 'localhost';
1079         }
1080
1081         public function getServerType( $i ) {
1082                 return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
1083         }
1084
1085         /**
1086          * @deprecated Since 1.30, no alternative
1087          */
1088         public function getServerInfo( $i ) {
1089                 wfDeprecated( __METHOD__, '1.30' );
1090                 if ( isset( $this->mServers[$i] ) ) {
1091                         return $this->mServers[$i];
1092                 } else {
1093                         return false;
1094                 }
1095         }
1096
1097         /**
1098          * @deprecated Since 1.30, construct new object
1099          */
1100         public function setServerInfo( $i, array $serverInfo ) {
1101                 wfDeprecated( __METHOD__, '1.30' );
1102                 $this->mServers[$i] = $serverInfo;
1103         }
1104
1105         public function getMasterPos() {
1106                 # If this entire request was served from a replica DB without opening a connection to the
1107                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1108                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1109                 if ( !$masterConn ) {
1110                         $serverCount = count( $this->mServers );
1111                         for ( $i = 1; $i < $serverCount; $i++ ) {
1112                                 $conn = $this->getAnyOpenConnection( $i );
1113                                 if ( $conn ) {
1114                                         return $conn->getReplicaPos();
1115                                 }
1116                         }
1117                 } else {
1118                         return $masterConn->getMasterPos();
1119                 }
1120
1121                 return false;
1122         }
1123
1124         public function disable() {
1125                 $this->closeAll();
1126                 $this->disabled = true;
1127         }
1128
1129         public function closeAll() {
1130                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1131                         $host = $conn->getServer();
1132                         $this->connLogger->debug( "Closing connection to database '$host'." );
1133                         $conn->close();
1134                 } );
1135
1136                 $this->mConns = [
1137                         self::KEY_LOCAL => [],
1138                         self::KEY_FOREIGN_INUSE => [],
1139                         self::KEY_FOREIGN_FREE => [],
1140                         self::KEY_LOCAL_NOROUND => [],
1141                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1142                         self::KEY_FOREIGN_FREE_NOROUND => []
1143                 ];
1144                 $this->connsOpened = 0;
1145         }
1146
1147         public function closeConnection( IDatabase $conn ) {
1148                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1149                 foreach ( $this->mConns as $type => $connsByServer ) {
1150                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1151                                 continue;
1152                         }
1153
1154                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1155                                 if ( $conn === $trackedConn ) {
1156                                         $host = $this->getServerName( $i );
1157                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1158                                         unset( $this->mConns[$type][$serverIndex][$i] );
1159                                         --$this->connsOpened;
1160                                         break 2;
1161                                 }
1162                         }
1163                 }
1164
1165                 $conn->close();
1166         }
1167
1168         public function commitAll( $fname = __METHOD__ ) {
1169                 $failures = [];
1170
1171                 $restore = ( $this->trxRoundId !== false );
1172                 $this->trxRoundId = false;
1173                 $this->forEachOpenConnection(
1174                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1175                                 try {
1176                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1177                                 } catch ( DBError $e ) {
1178                                         call_user_func( $this->errorLogger, $e );
1179                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1180                                 }
1181                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1182                                         $this->undoTransactionRoundFlags( $conn );
1183                                 }
1184                         }
1185                 );
1186
1187                 if ( $failures ) {
1188                         throw new DBExpectedError(
1189                                 null,
1190                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1191                         );
1192                 }
1193         }
1194
1195         public function finalizeMasterChanges() {
1196                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1197                         // Any error should cause all DB transactions to be rolled back together
1198                         $conn->setTrxEndCallbackSuppression( false );
1199                         $conn->runOnTransactionPreCommitCallbacks();
1200                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1201                         $conn->setTrxEndCallbackSuppression( true );
1202                 } );
1203         }
1204
1205         public function approveMasterChanges( array $options ) {
1206                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1207                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1208                         // If atomic sections or explicit transactions are still open, some caller must have
1209                         // caught an exception but failed to properly rollback any changes. Detect that and
1210                         // throw and error (causing rollback).
1211                         if ( $conn->explicitTrxActive() ) {
1212                                 throw new DBTransactionError(
1213                                         $conn,
1214                                         "Explicit transaction still active. A caller may have caught an error."
1215                                 );
1216                         }
1217                         // Assert that the time to replicate the transaction will be sane.
1218                         // If this fails, then all DB transactions will be rollback back together.
1219                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1220                         if ( $limit > 0 && $time > $limit ) {
1221                                 throw new DBTransactionSizeError(
1222                                         $conn,
1223                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1224                                         [ $time, $limit ]
1225                                 );
1226                         }
1227                         // If a connection sits idle while slow queries execute on another, that connection
1228                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1229                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1230                                 throw new DBTransactionError(
1231                                         $conn,
1232                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1233                                 );
1234                         }
1235                 } );
1236         }
1237
1238         public function beginMasterChanges( $fname = __METHOD__ ) {
1239                 if ( $this->trxRoundId !== false ) {
1240                         throw new DBTransactionError(
1241                                 null,
1242                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1243                         );
1244                 }
1245                 $this->trxRoundId = $fname;
1246
1247                 $failures = [];
1248                 $this->forEachOpenMasterConnection(
1249                         function ( Database $conn ) use ( $fname, &$failures ) {
1250                                 $conn->setTrxEndCallbackSuppression( true );
1251                                 try {
1252                                         $conn->flushSnapshot( $fname );
1253                                 } catch ( DBError $e ) {
1254                                         call_user_func( $this->errorLogger, $e );
1255                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1256                                 }
1257                                 $conn->setTrxEndCallbackSuppression( false );
1258                                 $this->applyTransactionRoundFlags( $conn );
1259                         }
1260                 );
1261
1262                 if ( $failures ) {
1263                         throw new DBExpectedError(
1264                                 null,
1265                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1266                         );
1267                 }
1268         }
1269
1270         public function commitMasterChanges( $fname = __METHOD__ ) {
1271                 $failures = [];
1272
1273                 /** @noinspection PhpUnusedLocalVariableInspection */
1274                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1275
1276                 $restore = ( $this->trxRoundId !== false );
1277                 $this->trxRoundId = false;
1278                 $this->forEachOpenMasterConnection(
1279                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1280                                 try {
1281                                         if ( $conn->writesOrCallbacksPending() ) {
1282                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1283                                         } elseif ( $restore ) {
1284                                                 $conn->flushSnapshot( $fname );
1285                                         }
1286                                 } catch ( DBError $e ) {
1287                                         call_user_func( $this->errorLogger, $e );
1288                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1289                                 }
1290                                 if ( $restore ) {
1291                                         $this->undoTransactionRoundFlags( $conn );
1292                                 }
1293                         }
1294                 );
1295
1296                 if ( $failures ) {
1297                         throw new DBExpectedError(
1298                                 null,
1299                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1300                         );
1301                 }
1302         }
1303
1304         public function runMasterPostTrxCallbacks( $type ) {
1305                 $e = null; // first exception
1306                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1307                         $conn->setTrxEndCallbackSuppression( false );
1308                         if ( $conn->writesOrCallbacksPending() ) {
1309                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1310                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1311                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1312                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1313                                 return;
1314                         } elseif ( $conn->trxLevel() ) {
1315                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1316                                 // thus leaving an implicit read-only transaction open at this point. It
1317                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1318                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1319                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1320                                 return;
1321                         }
1322                         try {
1323                                 $conn->runOnTransactionIdleCallbacks( $type );
1324                         } catch ( Exception $ex ) {
1325                                 $e = $e ?: $ex;
1326                         }
1327                         try {
1328                                 $conn->runTransactionListenerCallbacks( $type );
1329                         } catch ( Exception $ex ) {
1330                                 $e = $e ?: $ex;
1331                         }
1332                 } );
1333
1334                 return $e;
1335         }
1336
1337         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1338                 $restore = ( $this->trxRoundId !== false );
1339                 $this->trxRoundId = false;
1340                 $this->forEachOpenMasterConnection(
1341                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1342                                 if ( $conn->writesOrCallbacksPending() ) {
1343                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1344                                 }
1345                                 if ( $restore ) {
1346                                         $this->undoTransactionRoundFlags( $conn );
1347                                 }
1348                         }
1349                 );
1350         }
1351
1352         public function suppressTransactionEndCallbacks() {
1353                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1354                         $conn->setTrxEndCallbackSuppression( true );
1355                 } );
1356         }
1357
1358         /**
1359          * @param IDatabase $conn
1360          */
1361         private function applyTransactionRoundFlags( IDatabase $conn ) {
1362                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1363                         return; // transaction rounds do not apply to these connections
1364                 }
1365
1366                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1367                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1368                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1369                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1370                         // If config has explicitly requested DBO_TRX be either on or off by not
1371                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1372                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1373                 }
1374         }
1375
1376         /**
1377          * @param IDatabase $conn
1378          */
1379         private function undoTransactionRoundFlags( IDatabase $conn ) {
1380                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1381                         return; // transaction rounds do not apply to these connections
1382                 }
1383
1384                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1385                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1386                 }
1387         }
1388
1389         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1390                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1391                         $conn->flushSnapshot( __METHOD__ );
1392                 } );
1393         }
1394
1395         public function hasMasterConnection() {
1396                 return $this->isOpen( $this->getWriterIndex() );
1397         }
1398
1399         public function hasMasterChanges() {
1400                 $pending = 0;
1401                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1402                         $pending |= $conn->writesOrCallbacksPending();
1403                 } );
1404
1405                 return (bool)$pending;
1406         }
1407
1408         public function lastMasterChangeTimestamp() {
1409                 $lastTime = false;
1410                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1411                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1412                 } );
1413
1414                 return $lastTime;
1415         }
1416
1417         public function hasOrMadeRecentMasterChanges( $age = null ) {
1418                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1419
1420                 return ( $this->hasMasterChanges()
1421                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1422         }
1423
1424         public function pendingMasterChangeCallers() {
1425                 $fnames = [];
1426                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1427                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1428                 } );
1429
1430                 return $fnames;
1431         }
1432
1433         public function getLaggedReplicaMode( $domain = false ) {
1434                 // No-op if there is only one DB (also avoids recursion)
1435                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1436                         try {
1437                                 // See if laggedReplicaMode gets set
1438                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1439                                 $this->reuseConnection( $conn );
1440                         } catch ( DBConnectionError $e ) {
1441                                 // Avoid expensive re-connect attempts and failures
1442                                 $this->allReplicasDownMode = true;
1443                                 $this->laggedReplicaMode = true;
1444                         }
1445                 }
1446
1447                 return $this->laggedReplicaMode;
1448         }
1449
1450         /**
1451          * @param bool $domain
1452          * @return bool
1453          * @deprecated 1.28; use getLaggedReplicaMode()
1454          */
1455         public function getLaggedSlaveMode( $domain = false ) {
1456                 return $this->getLaggedReplicaMode( $domain );
1457         }
1458
1459         public function laggedReplicaUsed() {
1460                 return $this->laggedReplicaMode;
1461         }
1462
1463         /**
1464          * @return bool
1465          * @since 1.27
1466          * @deprecated Since 1.28; use laggedReplicaUsed()
1467          */
1468         public function laggedSlaveUsed() {
1469                 return $this->laggedReplicaUsed();
1470         }
1471
1472         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1473                 if ( $this->readOnlyReason !== false ) {
1474                         return $this->readOnlyReason;
1475                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1476                         if ( $this->allReplicasDownMode ) {
1477                                 return 'The database has been automatically locked ' .
1478                                         'until the replica database servers become available';
1479                         } else {
1480                                 return 'The database has been automatically locked ' .
1481                                         'while the replica database servers catch up to the master.';
1482                         }
1483                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1484                         return 'The database master is running in read-only mode.';
1485                 }
1486
1487                 return false;
1488         }
1489
1490         /**
1491          * @param string $domain Domain ID, or false for the current domain
1492          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1493          * @return bool
1494          */
1495         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1496                 $cache = $this->wanCache;
1497                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1498
1499                 return (bool)$cache->getWithSetCallback(
1500                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1501                         self::TTL_CACHE_READONLY,
1502                         function () use ( $domain, $conn ) {
1503                                 $old = $this->trxProfiler->setSilenced( true );
1504                                 try {
1505                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1506                                         $readOnly = (int)$dbw->serverIsReadOnly();
1507                                         if ( !$conn ) {
1508                                                 $this->reuseConnection( $dbw );
1509                                         }
1510                                 } catch ( DBError $e ) {
1511                                         $readOnly = 0;
1512                                 }
1513                                 $this->trxProfiler->setSilenced( $old );
1514                                 return $readOnly;
1515                         },
1516                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1517                 );
1518         }
1519
1520         public function allowLagged( $mode = null ) {
1521                 if ( $mode === null ) {
1522                         return $this->mAllowLagged;
1523                 }
1524                 $this->mAllowLagged = $mode;
1525
1526                 return $this->mAllowLagged;
1527         }
1528
1529         public function pingAll() {
1530                 $success = true;
1531                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1532                         if ( !$conn->ping() ) {
1533                                 $success = false;
1534                         }
1535                 } );
1536
1537                 return $success;
1538         }
1539
1540         public function forEachOpenConnection( $callback, array $params = [] ) {
1541                 foreach ( $this->mConns as $connsByServer ) {
1542                         foreach ( $connsByServer as $serverConns ) {
1543                                 foreach ( $serverConns as $conn ) {
1544                                         $mergedParams = array_merge( [ $conn ], $params );
1545                                         call_user_func_array( $callback, $mergedParams );
1546                                 }
1547                         }
1548                 }
1549         }
1550
1551         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1552                 $masterIndex = $this->getWriterIndex();
1553                 foreach ( $this->mConns as $connsByServer ) {
1554                         if ( isset( $connsByServer[$masterIndex] ) ) {
1555                                 /** @var IDatabase $conn */
1556                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1557                                         $mergedParams = array_merge( [ $conn ], $params );
1558                                         call_user_func_array( $callback, $mergedParams );
1559                                 }
1560                         }
1561                 }
1562         }
1563
1564         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1565                 foreach ( $this->mConns as $connsByServer ) {
1566                         foreach ( $connsByServer as $i => $serverConns ) {
1567                                 if ( $i === $this->getWriterIndex() ) {
1568                                         continue; // skip master
1569                                 }
1570                                 foreach ( $serverConns as $conn ) {
1571                                         $mergedParams = array_merge( [ $conn ], $params );
1572                                         call_user_func_array( $callback, $mergedParams );
1573                                 }
1574                         }
1575                 }
1576         }
1577
1578         public function getMaxLag( $domain = false ) {
1579                 $maxLag = -1;
1580                 $host = '';
1581                 $maxIndex = 0;
1582
1583                 if ( $this->getServerCount() <= 1 ) {
1584                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1585                 }
1586
1587                 $lagTimes = $this->getLagTimes( $domain );
1588                 foreach ( $lagTimes as $i => $lag ) {
1589                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1590                                 $maxLag = $lag;
1591                                 $host = $this->mServers[$i]['host'];
1592                                 $maxIndex = $i;
1593                         }
1594                 }
1595
1596                 return [ $host, $maxLag, $maxIndex ];
1597         }
1598
1599         public function getLagTimes( $domain = false ) {
1600                 if ( $this->getServerCount() <= 1 ) {
1601                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1602                 }
1603
1604                 $knownLagTimes = []; // map of (server index => 0 seconds)
1605                 $indexesWithLag = [];
1606                 foreach ( $this->mServers as $i => $server ) {
1607                         if ( empty( $server['is static'] ) ) {
1608                                 $indexesWithLag[] = $i; // DB server might have replication lag
1609                         } else {
1610                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1611                         }
1612                 }
1613
1614                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1615         }
1616
1617         public function safeGetLag( IDatabase $conn ) {
1618                 if ( $this->getServerCount() <= 1 ) {
1619                         return 0;
1620                 } else {
1621                         return $conn->getLag();
1622                 }
1623         }
1624
1625         /**
1626          * @param IDatabase $conn
1627          * @param DBMasterPos|bool $pos
1628          * @param int $timeout
1629          * @return bool
1630          */
1631         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1632                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1633                         return true; // server is not a replica DB
1634                 }
1635
1636                 if ( !$pos ) {
1637                         // Get the current master position, opening a connection if needed
1638                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1639                         if ( $masterConn ) {
1640                                 $pos = $masterConn->getMasterPos();
1641                         } else {
1642                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1643                                 $pos = $masterConn->getMasterPos();
1644                                 $this->closeConnection( $masterConn );
1645                         }
1646                 }
1647
1648                 if ( $pos instanceof DBMasterPos ) {
1649                         $result = $conn->masterPosWait( $pos, $timeout );
1650                         if ( $result == -1 || is_null( $result ) ) {
1651                                 $msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
1652                                 $this->replLogger->warning( $msg,
1653                                         [ 'host' => $conn->getServer(), 'pos' => $pos ] );
1654                                 $ok = false;
1655                         } else {
1656                                 $this->replLogger->info( __METHOD__ . ': Done' );
1657                                 $ok = true;
1658                         }
1659                 } else {
1660                         $ok = false; // something is misconfigured
1661                         $this->replLogger->error( 'Could not get master pos for {host}',
1662                                 [ 'host' => $conn->getServer() ] );
1663                 }
1664
1665                 return $ok;
1666         }
1667
1668         public function setTransactionListener( $name, callable $callback = null ) {
1669                 if ( $callback ) {
1670                         $this->trxRecurringCallbacks[$name] = $callback;
1671                 } else {
1672                         unset( $this->trxRecurringCallbacks[$name] );
1673                 }
1674                 $this->forEachOpenMasterConnection(
1675                         function ( IDatabase $conn ) use ( $name, $callback ) {
1676                                 $conn->setTransactionListener( $name, $callback );
1677                         }
1678                 );
1679         }
1680
1681         public function setTableAliases( array $aliases ) {
1682                 $this->tableAliases = $aliases;
1683         }
1684
1685         public function setDomainPrefix( $prefix ) {
1686                 // Find connections to explicit foreign domains still marked as in-use...
1687                 $domainsInUse = [];
1688                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1689                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1690                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1691                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1692                                 $domainsInUse[] = $conn->getDomainID();
1693                         }
1694                 } );
1695
1696                 // Do not switch connections to explicit foreign domains unless marked as safe
1697                 if ( $domainsInUse ) {
1698                         $domains = implode( ', ', $domainsInUse );
1699                         throw new DBUnexpectedError( null,
1700                                 "Foreign domain connections are still in use ($domains)." );
1701                 }
1702
1703                 $this->localDomain = new DatabaseDomain(
1704                         $this->localDomain->getDatabase(),
1705                         null,
1706                         $prefix
1707                 );
1708
1709                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1710                         $db->tablePrefix( $prefix );
1711                 } );
1712         }
1713
1714         /**
1715          * Make PHP ignore user aborts/disconnects until the returned
1716          * value leaves scope. This returns null and does nothing in CLI mode.
1717          *
1718          * @return ScopedCallback|null
1719          */
1720         final protected function getScopedPHPBehaviorForCommit() {
1721                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1722                         $old = ignore_user_abort( true ); // avoid half-finished operations
1723                         return new ScopedCallback( function () use ( $old ) {
1724                                 ignore_user_abort( $old );
1725                         } );
1726                 }
1727
1728                 return null;
1729         }
1730
1731         function __destruct() {
1732                 // Avoid connection leaks for sanity
1733                 $this->disable();
1734         }
1735 }
1736
1737 class_alias( LoadBalancer::class, 'LoadBalancer' );